Campbell recently returned to Loftus Road after a successful loan spell with Ipswich, who are keen to sign him permanently, while Cardiff and Bolton have also been linked.
The arrival of Loic Remy at QPR has pushed Campbell further down the pecking order as Harry Redknapp's side fight for Premier League survival.
And Holloway said: "Have I rung Harry Redknapp? Yeah. Does that mean I'm going to get him? No. Am I fighting for him? Yeah. Will I get him? I don't know.
"But it's him and AN Other. There are lots of other players I could get.
"I think deals which get done you should talk about but deals that don't, you shouldn't.
"I never promise the fans anything I can't produce. I remember the Quincy Jones song The Dude, 'don't let your mouth write a cheque that your body can't cash'. That's what I don't like doing.
"I'm trying my best, the board are trying their best to add to the group and we know time is ticking."